Transmission control



Aug. 21, 1928. 1,681,532

v F. G. GARDNER TRANSMISSION CONTROL 'bi/WA@ Aug. 2l, 1928.

Filed July 2, 1925 1,681,532 F. G. GARDNER TRANSMI S S ION CONTROL 3 Sheets-Sheet 3 Patented Aug. 21, 1928.

UNITED STATES PATENT OFFICE.

FRED G. GARDNER, F NEW YORK, N. Y., ASSIGNOB TO WESTERN ELECTRIC COMPANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TRANSMISSION CONTROL.

Application illed J'uly 2,

This invention relates to transmissioncom trol in a signaling system such asa multiplex carrier current telephonefor telegraph system.

The transmission characteristics of a circuit or line vary not only with the frequency of the transmitted currents but also with the :hanging conditions of weather, temperature, etc.

ln order, therefore, that the transmission eiiciency of a circuit or line may be maintained substantially constant, provision must be made to compensate for theseI varylng conditions.

rlhis may be accomplished by maintaining substantially constant the output energy of the translating devices employed in the system.

Among the objects of the invention are:

To maintain the output energy of a. translating device at a substantially constant value, irrespective of varying operating conditions.

To provide a gain control system wherein the input energy to a repeater is maintained substantially constant by varying the inductive coupling between the line and the repeater input in accordance with changes in .line attenuation.

ln accordance with this invention, which is particularly applicable to carrier current signaling systems as well as to ordinary speech trequency and other signaling systems, the input and output of the various translating devices employed at the terminal and intermediate stations are maintained 'substantially constant by automatically vary` ing the coupling between such devices and the line circuit to compensate for changes in attenuation.

The invention will be described as applied to a multiplex carrier current telephone system, although it will be understood that it may also be applied to other signaling systems.

ln the drawings,

Fig. l shows diagrammatically the apparatus of one terminal and a repeater station of a multiplex carrier telephone system.

Fig. 2 shows diagrammatically a pilot frequency oscillator and the apparatus for frequency range.

1923, serial N0. 648,868.

maintaining the output thereof substantially constant.

Fig. 3 shows diagrammatically the means employed between t e receiving channels and the main line for automatically compensatlngv'for changing attenuation of the line.

1g. 4 shows curves representing the transformation ratio characteristics of the compensator input transformer at diiierent frequencies for different degrees of coupling.

Fig. 5 shows diagrammatically one of the amplifiers of the repeater station and the apparatus for maintaining the input and output thereof substantially constant.

Fig. 1 shows a main line ML to which, at the left, is connected the apparatus for one termlnal of a multiplex carrier current telephone system, and at the right, a twoway carrier current repeater.

The main line ML is adapted to transmit low frequency currents, suc'h as voic'e currents, as well as high frequency currents, such as carrier currents.

The high and low frequency currents are separated at the terminal by means o`f high and low pass filters HPF and LPF so that only the low frequency currents pass to the low frequency line L and only the high frequency currents pass to the carrier current terminal apparatus.

Temi/nal apparatus.

The terminal carrier current apparatus comprises a plurality of transmitting channels TCl, TG2, etc. connected through a lcommon transmitting channel CTC to the main line ML, and a plurality of receiving channels RC1, RC2, etc. connected through a comni receiving channel CRC to the main line 1V The channel carrier frequencies for trans- :mission in one direction are within one frequency range and those for transmission in the opposite direction are Within another 'The oppositely directed transmissions are separated at the terminal by means of directional filters TDF and RDF which are respectively high pass and low pass filters of the type disclosed in U. S. patnt to Campbell No. 1,227,113, May 22, 19

' TBF1.

The modulator M1 may be of aly well known type such as the balanced mo ulator disclosed in U. S. patent to Carson, N o. 1,343,307, J une 15, 1920.

Carrier currents of the frequency assigned to channel TG1, are supplied from a source- TO1 to the modulator M1 wherein they are modulated by voice frequency currents or other signaling currents rom a source such as a transmitter T1.

The band ilter TBF1, may be of anywell own type such as that disclosed in the Campbell patent, supra. It is designed to pass currents of frequencies within either the upperUor lower side band of the carrier frequency assigned to this channel and to suppress currents of all other frequencies.

The several receiving channels are similar, the apparatus thereof differing merely on account of the different carrier frequencies employed, so a description of one channel will suice.

The receiving channel RC1, includes a/receiving band filter RBF1, and a demodulator DM The band filter RBF1, which is of the same type as the filter TBF1, is designed to pass currents of frequencies within the upper or the lower side band of the carrier frequency assigned to this channel andto suppress currents-of all other frequencies.

The demodulator DM1 may be of any well known type such as the balanced demodulator disclosed in U. S. patent to Carson, No. 1,343,308, June 15, 1920. Currents selected by the band filter RBF1 are delivered to the demodulator DM1 wherein they react with currents of the carrier frequency assigned to the channel supplied from a source R01. The voice or other signaling currents thus detected in the demodulator DM1 are delivered to a receiver Pilot frequency channel.

'oscillator PO comprises a three-electrode electronic valve having in a branch of the plate circuit thereof a frequency determining circuit 6 inductively coupled to the grid circuit. The output branch 7 of the plate circuit is coupled to a work circuit 8 by means of a constant current transformer 9 to be described presently. The output of the .oscillator may be regulated to the desired former 11, having a closed circuit secondary winding carried by one end of a pivoted lever 12 which at its other end carries the secondary winding of the transformer 9. The pivoted lever, preferably, is made of non-magnetic material. Current for the primary winding of transformer 11 is supplied from the oscillator PC through a coupling coil 13 and an amplifier PFA.

Current traversing t e primary winding of transformer 11 induces a currentin the closed circuit secondary so that the secondary tends to move away from the primary winding and will move away unless restrained as by a spring 14. The tension of spring 14 is so adjusted that the pull of the spring will just balance the force of repulsion between the windings of transformer 11 when the output of the oscillator is the desired amount.

If the oscillator output tends to decrease below the desired amount, less current will be delivered to the primary of transformer 11 thereby reducing the repulsion between the windings. The spring 14 thereupon moves the secondaries of both transformers 9 and 11 closer to their respective primary windings so that the coupling therebetween becomes closer. This movement continues until a balance is reestablished between the pull of spring 14.- and the repulsion between the windings of transformer 11.

The closer coupling of the windings of transformer 9 increases the ratio of transformation thereof so as to compensate for the tendency of the oscillator output to decrease.

Should the oscillator output tend to increase. above the desired amount, the repul sionbetween the windings of transformer 11 overcomes the pull of spring 14 and loosens the ,coupling between the windings of transfdnmer 9 to compensate for the tendency of the oscillator output to increase.

The pilot frequency selector circuit PFS may comprise a simple coupling transformer sage of currents of all other frequencies.

Receiving chan/ncl attenuation compensator.

V The common receiving channel CRC contains means to compensate for changes in line attenuation.

Such compensating means, indicated in Fig. 1 by the rectangle 18 and shown dia grammatically in Fig. 3, includes an input constant current transformer 20, a potentiometer 21, apilot frequency selecting circuit PFS1, a pilot frequency amplifier PFA1, and a control transformer 22.

The primary winding of transformer 20 is connected to the receiving directional filter RDF, and the output leads 23 of the compensator are connected to the common receiving channel extending to the individual receiving channels.

The constant current transformer 20 has a core along one leg of which the secondary winding is movable with respect to the primary winding. The secondary'winding of transformer 20 is carried by one end of a pivoted lever 24 of non-inductive conductmg material. The pivoted lever 24 carries at its other end, the closed circuit secondary winding of transformer 22 which is movable with respect to the primary winding along one leg of the core thereof. i

The pilot frequency selecting circuit PFSI, is similar to the selecting circuit PFS previously described in connection with Fig. 2 and differing therefrom merely in itsI constants to make it selective for a different pilot frequency. d

The pilot frequency amplifier PFA, may

l be of any well known type such as a threeelectrode electronic amplifier to be described in connection with Fig. 5.

The setting of the potentiometer 21 is automatically controlled by the pivoted lever 24.

The potentiometer operating mechanism controlled by pivoted lever 24 includes a movable contact arm 25 secured to a shaft 26 which has two ratchet wheels 27 and 28 mounted thereon An operating magnet 29 having a self-interrupting circuit is provided with a pawl 30 for engaging the ratchet wheel 27 to move the shaft 26 and movable contact arm 25 in a clockwise direction. Movement of shaft 26 and contact arm 25 in a counter-clockwise direction is effected by the ratchet wheel 28 and its operating magnet 31 and pawl 32. The operating circuit of magnets 29 and 31 are completed through the respective contacts 33 and 34 on the pivoted lever.

The tension of spring 35 is so adjusted attenuation of the line.

that the pull thereof'will justobalance the force of repulsion between the windin s of' transformer 22 for a certain strengti of jreceived current corresponding to a certain If the attenuation characteristic of the line increases, there is an increased attenuation of ,the currents of all frequencies traversing the line. The' amount of current of the pilot frequency incoming to the rimary winding of transformer 20 there ore decreases so that the input to the pilot frequency amplifier de! creases. Consequently less current is delivered to the primary winding of trausformer 22 whereby less current is induced in the secondary thereof. The repulsion between the windings of transformer 22 therefore, decreases so that the pull of spring 35 predominates causing the pivoted lever 24 to move in a counter-clocltwise direction until the pull of spring 35 is again balanced by the repulsion between the transformer windings. The counter-clockwise movement of pivoted lever 24 makes the coupling between the windings of transformer 2() closer thereby increasing the ratio of transfornmtion thereof. Thus the amount of current induced in the secondary winding of transformer 2O increases to compensate for the in creased attenuation of the line.

Iffthe change in line attenuation characteristie is such as to decrease the attenuation of the currents traversing the line the pivoted lever 24 will be moved in a clockwise direction to loosen the .coupling between the windings of transformer 20 to compensate for the charge in attenuation.

If the change in attenuation is slight, the correction or compensation thereof l.: taken care of solely b v varying the coupling between the windings of the input transformer. However, if the change is greater than can be taken care of in this manner, the potentiometer control then comes into play.

Thus, should the attenuation increase to a considerable extent, the counter-clockwise movement of the pivoted. lever 24 will be sufficient to close contact 33. The closure of this contact completes the operating circuit for actuating magnet 29 which thereupon 115 spring 35 and the repulsion between the 125 windings of the transformer. Contact 33 thereupon opens, restoring the potentiometer operating mechanism to normal condition.

Thereafter slight changes in attenuation are taken care of solely by automatically varying the coupling between the windings of the input transformer 20 in the manner previously described.

Should the attenuation of the line decrease to a considerable extent, the resulting increased input current to the compensator will cause a sufficient clockwise movement of the pivoted lever 24 to close contact 34. Operating magnet 31 then causes its pawl 32 to intermittently engage ratchet wheel 28 to move shaft 26 and its movable contact arm 25 in a counter-clockwise direction.

The movement of the contact arm 25 in a counter-clockwise direction continues until the setting of the potentiometer compensates for the change in attenuation.

)The characteristics of input transformer 20 are such that when the coupling between its windings is' changed, there is a greater change in its current ratio of transformation for high frequencies than for low frequencies. This is shown graphically in Fig. 4 wherein several curves representing different degrees of coupling between the transformer windings have been plotted with current ratio of transformation as ordinates against frequencies as abscissae.

Inspection of Fig. 4 shows that for frequencies betwen f and f', if the coupling between the transformer windings is increased the ratio of transformation for the higher frequencies is increased more than for the lower frequencies within the range of frequencies being transmitted. If the coupling is loosened, the higher frequencies will likewise be affected more than the lower frequencies. Therefore, by changing the degree of coupling between its windings, the input transformer is made to serve as an attenuation equalizer.

i Repeater.

The two-way repeater shown at the right in Fig. 1 comprises two one-way repeatlng channels RW and RE.

Attenuated currents incoming from section WV of the main line NIL are amplified in the repeating channel RW which delivers the amplified currents to section E of the main line. Similarly, attenuated currents incoming from main line section E are amplified in repeating channel RE and the amplified currents are then delivered to main line section W.

The input and output directional filters TIF and lVOF are high pass filters Which may be of any well known type such as the type disclosed in U. S. Patent to Raibourn No. 1,413,357, dated April 18, 1922. These filters are designed to pass currents of the frequencies to be amplified in the repeater channel RW and to suppress currents of lower frequencies.

The amplifier WA may be of any well known type but as illustrated herein is a two-stage balanced amplifier which is shown in detail in Fig. 5.

' The repeating channel RE includes inputand output directional filters EIF and EOF `are designed to pass currents of 'the frequencies to be amplified iu the receivin channel RE and to suppress currents o higher frequencies. v

The amplifier EA is like that employed in repeating channel RW which will be later described in connection with Fig. 5.

The amplifier of Fig. 5 includes two single stage amplifying structures 40 and 41 connected in tandem through an interstage variable attenuation equalizer 42 and a compensator 43 to compensate for changes in line attenuation. y

Each of the single stage amplifying structures may be of any well known type, such as a balanced amplifying structure, similar to that disclosed in Fig. 1 of U. S. patent to Colpitts, No. 1,128,292, February 16, 1915, but it must bc adapted to handle the wide range of frequencies encountered in a carrier current system.

The attenuation equalizer 42 is a balanced equalizer comprising an inductance 44 shunted by a capacity 45 connected in series with two variable resistance networks 46 and 47. This attenuation equalizer`serves to so connect the two single stage amplifying struclun tures as to equalize diflerencies in line attenuation at the different frequencies of the currents to be amplified thus giving outputs from the amplifiers of substantially equal value for the different frequencies.

Inductance 44 and capacity 45 form a loop circuit tuned to a frequency higher than, or approximately equal to, the highest frequency that is to be repeated.

The midpoint of the inductance 44 is con- :ted to the common branch of the input circuits of the amplifying structure 41.

The two resistances 46 and 47 of the variable attenuation equalizer 42 are arranged to be varied simultaneously. This attenuationl equalizer serves to attenuate the lower frequencies more than the higher frequencies. The attenuation at the higher frequencies lremains substantially constant for different values of resistance in series with the tuned loop circuit. However, the attenuation at the lower frequencies decreases with increase of resistance and increases with decrease of resistance. The reason for this may be explained as follows: It is well known that a lcop circuit having inductance and capacity offers very high impedance at the resonant frequency. The impedance of such a loop at frequencies other than the resonant frequency decreases rapidly as the frequency is decreased or increased. When resistance is included in series with the tuned loop circuit, the resistanceitself offers the same impedance at all frequencies, and the total impedance becomes greater. However, the increase in impedance at the resonant frequency is slight While the increase in impedance at other frequencies is great.

The compensator 43 is similar to that shown in Fig. 3 hereinbefore described. It includes an input constant current transformer 20, a balanced potentiometer 50, a pilot frequency selecting circuit PFS2 tuned to the frequency of pilot frequency oscillator PO, a pilot frequency amplifier PFA2 and transformer 22.

The secondary windings of transformers 20 and 22 are carried at the opposite ends of the pivoted lever 24. This p ivotcd lever controls operating mechanismfor adjusting the settin of the balanced potentiometer 50 and for a'djusting the setting of the variable attenuation equalizer resistances 46 and 47.

The operation of the compensator and variable attenuation equalizer associated with the amplifier of repeating channel RW and shown in Fig. 5 will now be described.

Assuming that the attenuation of line section W increases, the magnitude of the energy at all frequencies traversing the primary winding of input transformer 20 decreases. If this decrease is slight, the correction therefor will be taken care of solely by closer coupling of the windings of the input transformer 20 in the manner described, in connection with Fig. 3.

However, if the attenuation increases to such an extent that closer coupling of transformer 20 does not fully compensate therefor, the operating mechanism of the balanced potentiometer 5() and the variable attenuation equalizer 42 then comes into play to change the settings of the potentiometer 50 and the attenuation equalizer 42.

The changed settin of potentiometer 50 is such as to increase the input energy to the amplifiers at all frequencies. Changing the setting of resistances 46 and 47 by adjusting the contact arms 48 and 49 increases the amount of resistance in series with the tuned loop circuit of the variable attenuation equalizer, thus increasing the attenuation of the lower frequencies with respect to the high lfrequencies of the band of frequencies being transmitted.

The input transformer 20, potentiometer 50 and variable attenuation equalizer 42 are so related that the compensation effected by a one-step change of potentiometer 50 and of variable attenuation equalizer 42 is slightly greater than that effected by the entire change in the coupling of input transformer Therefore, when the settings of potentiometer 50 and variable attenuation equalizer 42 have been changed in the process of compensatin for an increase inline attenuation, the coup 'ng of the windings of input transformer 2O is automatically loosened until the correct conditions exist to fully and substantially exactly compensate for the increase in line attenuation.

Should the line attenuation decrease, the input coil 20, potentiometer 50 and variable attenuation equalizer 42 cooperate to conipensate therefor.

The invention set forth herein is, of course, susceptible of various other modifications and adaptations.

What is claimed is:

1. A translating device having input and output circuits, an incoming circuit, an inductive coupling between the incoming circuit and the input circuit, and means connected to the output circuit to regulate the inductive relation of said coupling between the incoming circuit and the input circuit.

2. A translating device having input and output circuits, an incoming circuit, windings comprising an inductive coupling between the incoming circuit and the input circuit, and means controlled by the output of said device for regulating the inductive relation of said windings.

3. An amplifier having input and output circuits, a constant current transformer coupling the input circuit to an incoming circuit, and means controlled by the output of the amplifier to vary the ratio of transformation of said transformer.

4. The combination of an amplifier, an external circuit coupled thereto by a constant current transformer, and means controlled by the amplifier output to vary the ratio of transformation of said transformer.

5. In a multiplex carrier current system, a repeater for amplifying attenuated currents of different frequencies from an incoming line section and delivering the ampliiied currents to an outgoing line section, said repeater including a two-stage amplifier rovided with an iuterstage attenuation equa `zer, and means controlled by the repeater output to vary the setting of the attenuation equalizer to compensate for attenuation of the incoming line section.

6. In a carrier current system, an amplifying repeater for amplifying attenuated currents of different frequencies from an incoming line section and delivering the ainplified current to an outgoing line section, coupling means between the incoming line section and the repeater, a potentiometer between the coupling means and the repeater, and means controlled by the repeater output to vary the degree of coupling of said cou ling means and to change the setting of t e potentiometer.

7. In a multiplex carrier current system, a repeater for amplifying attenuated currents of different frequencies from an incoming line section and delivering the ampliied currents to'an outgoing line sectlon, said repeater including a two-stage amplifier provided with an-interstage attenuation equalizer, coupling means between the incoming line section and the repeater,'and means controlled by the repeater output to vary the degree of coupling of said amplifying means and to vary the setting of the attenuation e ualizer.

8. In a mu tiplex carrier current system, a repeater for amplifying attenuated cur'- rents of different frequencies from an incoming line section and delivering the amplied currents to an outgoing line section, said repeater including a two-stage amplifier provided with an interstage attenuation cqualizer coupling means between the incoming line section and the repeater, a

potentiometer between the coupling means and the repeater, and means controlled by the repeater output to vary the degree of coupling of said coupling means and to vary .input circuit to said transmission line, and

means controlled by said carrier Wave to vary the ratio of transformation of said transformer.

10. In a system of transmission regulation, a .variable transmission line over which a pilot wave and signalling Waves are transmitted, a. repeater having input and outputcircuits and including a two-stage amplifier provided With an mterstage attenuation equalizer, means for coupling said input circuit to said transmission line, and means in said output circuit controlled by said pilot Wave to vary the degree of coupling of said amplifier 4and to vary the adjustment of said attenuation equalizer.

In Witness'whereof, I hereunto subscribe my name this 25th da of June, A. D. 1923.

FR D G. GARDNER. 

